1. Field of the Invention
The present invention relates to a turn signal switch device attached to a steering column or the like of an automobile and serving as a direction indicator and, more specifically, it relates to a mechanism for releasing an excess load when, in a cancel operation for automatically restoring an operating lever provided in the turn signal switch device from an operating position to a neutral position, a force preventing the automatic restoring is applied to the operating lever.
2. Description of the Related Art
In the turn signal switch device of an automobile, the base end of an operating lever is rotatably supported by a housing integrally formed with the steering column or the like, and the forward end of this operating lever is rotated from a neutral position to a right or left direction indicating position, whereby a right-turn or left-turn lamp is caused to blink. In such a turn signal switch device, to retain the operating lever at three positions: the right and left direction indicating positions and the neutral position, the inner surface of the housing is provided with a cam surface, and the operating lever is provided, through the intermediation of a spring, with a driving member to be engaged with the cam surface. Further, there is provided a cancel mechanism for automatically restoring the operating lever to the neutral position when the steering wheel is turned in a direction opposite to the indicated direction, with the operating lever rotated to the right or left direction indicating position.
A known conventional example of this cancel mechanism is disclosed in Japanese Patent Unexamined Application Publication U.S. Pat. No. 5,949,040, which was proposed by the present applicant. FIG. 9 is a cross sectional view schematically showing the construction of the turn signal switch device disclosed in the above-mentioned publication, FIG. 10 is a front view of a movable member provided in the turn signal switch device, and FIGS. 11A and 11B are schematic diagrams illustrating the operation of a cancel mechanism provided in the turn signal switch device.
In these drawings, numeral 100 indicates a housing. The housing 100 is secured to a column cover, a combination switch, etc. (not shown) which is a stator member of a steering device. On the inner bottom surface of the housing 100, a guide shaft 101 and a support shaft 102 are provided at a predetermined interval. The guide shaft 101 is fitted into a first elongated hole 103a of a first lever member 103, and a second lever member 104 is rotatably supported by the support shaft 102. The first lever member 103 has a second elongated hole 103b, into which a connection pin 104a provided on the second lever member 104 is fitted. Further, at the front and rear ends of the first lever member 103, there are provided an abutting portion 103c and a cam portion 103d, the cross sectional configuration of the cam portion 103d being semi-circular. The first lever member 103 is engaged with one arm of a torsion coil spring 105, by means of which the first lever member 103 is elastically biased in the longitudinal direction of the elongated holes 103a and 103b. A winding portion of the torsion coil spring 105 is inserted into a boss 106 provided on the inner bottom surface of the housing 100, and the other arm thereof is engaged with the side wall of the housing 100. Further, the second lever member 104 has a first opening 104b and a second opening 104c, and the openings 104b and 104c are opposed to each other through a support shaft 105.
An operating lever 107 is supported by the housing 100 such that it is rotable around a support shaft 108 in the directions indicated by the arrows A and B, and inside the housing 100, there is formed a V-shaped cam surface 109 having a pair of lock portions 109a on the right and left sides. A holder 110 is mounted to the operating lever 107, and the operating lever 107 and the holder 110 integrally rotate horizontally around a straight line connecting the support shafts 108. Inside a cylindrical portion 110a protruding on the front side of the holder 110, a driving member 111 is slidably held, and the forward end of this driving member 111 is constantly held in press contact with the cam surface 109 by a spring (not shown). Further, a movable member 115 is rotatably supported by the cylindrical portion 110a of the holder 110, and both arms of a return spring 116 wound around the movable member 115 are engaged with the holder 110, whereby the movable member 115 is constantly biased toward the central stable position. Further, a cam portion 112 having a semi-circular cross sectional configuration and a receiving portion 113 hang down from the movable member 115, and the cam portion 112 is opposed to the cam portion 103d of the first lever member 103, the receiving portion 113 reaching the interior of the second opening 104c of the second lever member 104.
In the turn signal switch device, constructed as described above, when the operating lever 107 is at the neutral position, the forward end of the driving member 111 abuts the central valley of the cam surface 109, and is stably held at the position by the elasticity of a spring (not shown). At this time, as shown in FIG. 11A, the cam portion 112 on the operating lever 107 side and the cam portion 103d of the first lever member 103 are in contact with each other at their apexes, and the first lever member 103 retracts against the biasing force of the torsion coil spring 105. Thus, the abutting portion 103c of the first lever 103 is positioned outside the rotation path of a cancel protrusion 114 rotating with the steering wheel; if the steering wheel is turned in this condition, the cancel protrusion 114 does not abut the abutting portion 103c of the first lever member 103, and the operating lever 107 is maintained at the neutral position.
When the operating lever 107 is rotated from this neutral position in the direction of the arrow A or the arrow B, the forward end of the driving member 111 moves over the slope of the cam surface 109 and is engaged with the lock portion 109a, and stably held at the position by the lock portion 109a. For example, when the operating lever 107 is rotated in the direction of the arrow B, the movable member 115 integrally rotates with that, and the cam portion 112 and the receiving portion 113 of the movable member 115 are displaced from the position shown in FIG. 11A to that shown in FIG. 11B. As a result, the cam portion 112 is detached from the apex of the cam portion 103d of the first lever member 103, and the first lever member 103 receives the elastic force of the torsion coil spring to advance along the longitudinal direction of the elongated holes 103a and 103b, the abutting portion 103c advancing into the rotation path of the cancel protrusion 114. Further, with the rotation in the direction of the arrow B of the operating lever 107, switching operation is effected on a contact (not shown), and the right-hand turn lamp blinks.
In the right-hand turn state shown in FIG. 11B, when the steering wheel is turned in the opposite direction (the direction of the arrow in the drawing), the cancel protrusion 114 abuts the abutting portion 103c of the first lever member 103 during the return operation. As a result, the first lever member 103 rotates clockwise as seen in the drawing around the guide shaft 101, and the torque is transmitted from the second elongated hole 103b to a second lever member 104 through a connection pin 104a, and the second lever member 104 rotates clockwise around the support shaft 102, so that the second opening 104C of the second lever member 104 is rotated and displaced upward as seen in the drawing. As a result, the periphery of the second opening 104C upwardly pressurizes the receiving portion 113 of the movable member 115, so that the driving member 111 is detached from the lock portion 109a of the cam surface 109 and moves toward the central valley, and the operating lever 107 and the first and second lever members 103 and 104 are automatically restored to the central position shown in FIG. 11A.
Further, in the right-hand turn state shown in FIG. 11B, when some force preventing the automatic restoration is applied to the operating lever 107, for example, when the steering wheel is turned in the opposite direction, with the operating lever 107 being pressed by the driver, the periphery of the second opening 104C upwardly pressurizes the receiving portion 113 of the movable member 115 as described above. However, the operating lever 107, which is being pressed, is not automatically restored. In this case, the movable member 115 rotates the peripheral surface of the cylindrical portion 110a of the holder 110 from the stable position to the retracted position against the biasing force of the return spring 116. And, when the cancel protrusion 114 passes the abutting portion 103c of the first lever member 103, the movable member 115 is automatically restored from the retracted position to the stable position by the biasing force of the return spring 116, so that it is maintained in the right-hand turn state shown in FIG. 11B again.
In the conventional turn signal switch device, constructed as described above, when some force preventing automatic restoration is applied to the operating lever 107 when automatically restoring the operating lever 107 from the operating position to the neutral position, an excess load generated between the second opening 104C of the second lever member 104 and the receiving portion 113 of the movable member 115 is released (absorbed) by the rotation of the movable member 115, so that it is possible to prevent breakage of the power transmission system including the first and second lever members 103 and 104 and the receiving portion 113. However, to install such a mechanism, it is necessary to provide the rotatable movable member 115 and the return spring 116 which elastically biases the movable member 115 toward the stable position, and the number of parts increases due to the movable member 115 and the return spring 116. Further, due to the mounting space for the movable member 115 and the return spring 116, the size of the turn signal switch device is enlarged.